What is "deconfliction"? Russia says it has suspended Syrian airspace agreement with US.

Russia has suspended its "deconfliction" agreement with the United States in the wake of the missile strike against a Syrian air base President Donald Trump ordered in response to a devastating chemical attack that left dozens of civilians dead, the Kremlin announced Friday.

"Russia suspends the Memorandum of Understanding on Prevention of Flight Safety Incidents in the course of operations in Syria signed with the U.S.," according to a Russian foreign ministry statement.

Despite the announcement, U.S. officials said on Friday afternoon that the so-called deconfliction line was still operational and that the two countries have remained in contact.

Russian President Vladimir Putin — Syria's strongest ally — condemned the U.S. air raid this week as an "act of aggression against a sovereign state in violation of the norms of international law."

"This move by Washington has dealt a serious blow to Russian-U.S. relations, which are already in a poor state," Dmitry Peskov, a Putin spokesman, said after the attack.

What is the "deconfliction" agreement?

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The deconfliction line is a channel that allows the U.S. and Russia — who back different sides in the Syrian civil war — to coordinate their military actions in Syria's busy airspace and prevent collisions and other accidents.

The memorandum of understanding was signed by the two countries in 2015, after Russia began conducting strikes in Syria.

The U.S. used it to warn Russia ahead of its strike against the Syrian air base.

What will it mean if the deconfliction line is closed?

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Suspending the deconfliction agreement would further sour the relationship between the U.S. and Russia — and indicate that the Kremlin was serious when it blasted the U.S. airstrike.

It would also complicate American efforts to topple ISIS, adding concerns of collisions with Russian forces.

"It boxes in the U.S. ability to move against targets of opportunity," Nicholas Heras of the Center for New American Security told Mother Jones. "This would have a very real impact on the U.S. strategy against ISIS in Syria."